1. Technical Field
This disclosure generally relates to an object of creating a low energy refiner plate combination which operates on a fundamental concept similar to “pumping low energy plates.” The low energy refiner plate combination uses mechanical forces to increase the forward flow of pulp material in the refining gap, while also being reversible. The present invention relates to a system for refining lignocellulosic material, including a first stator plate segment refining zone and a first rotor plate segment refining zone, each of which have grooves. The rotor plate groove width is greater (wider) than the corresponding stator plate groove width at a corresponding distance measured from the inner edge of the refining area (rotor or stator plates) to the outer edge of the refiner plate (rotor or stator).
2. Related Art
There is generally a need for developing refiner plates for mechanical pulping processes that allow for a reduction in energy consumption during refining. One attempt at such development has involved the use of significantly coarser refiner plates, which increase refining intensity, but success has been limited. For example, it is believed that these plates produce poor pulp properties, and the energy savings achieved are usually quite limited.
In the 1990s, directional refiner plates were developed. Several versions of these plates exist, many of which use what is known in the art as bar “pumping angles” (also sometimes referred to as “feeding angles” or “bar angles”). Pumping angles are the angles formed by the bars relative to a central axis extending radially from the axis of rotation to the outer periphery of the plate, or relative to another radial line, so that in addition to causing refining impulses on a fiber mat, the bars and grooves are also used to promote pumping of the fiber material over the refiner plate segments. This design can reduce the time in which the fibers are retained in the refiner (frequently referred to as retention time), causing the fiber mat to be thinner and resulting in higher energy efficiency.
Although energy savings are appealing, many mechanical pulp mills have been unable to use conventional energy saving technology because their raw materials, which may contain too many contaminants and abrasives, are undesirable with such systems. A high level of contaminants or abrasives may also shorten the lifetime of a refiner plate. If refiner plates deteriorate (e.g., round over) through exposure to excessive amounts of abrasives or contaminants, pulp quality can deteriorate extremely fast. This forces the mill to change refiner plates frequently, making use of such plates economically impractical. To counter this wear problem, some mills reverse the direction of rotation of the refiner plates, e.g., every few days, to allow the edges of the bars on the plates to remain sharp for longer periods of time.
Accordingly, there is a need for an improved technology that would allow a mill to reverse the direction of rotation of its refiner plates, thus facilitating a benefit from the low energy refiner plate technology, while maintaining an acceptable wear life. It is to this need and others that the present disclosure is directed.